1. Field of the Invention
The present invention relates to an ultrasonic imaging apparatus using a digital control technique.
2. Description of Prior Art
In an ultrasonic imaging apparatus, ultrasonic beams are generated by exciting a transducer array having a plurality of transducer elements, and are then transmitted to an object under examination, e.g., a body, after being steered and focused. Ultrasonic echoes reflected from various internal portions of the body or organs are received by the transducer and are thereafter converted into ultrasonic beam signals. These signals are processed by the known circuits so as to display tomographic images of the desired internal portions of the body. To obtain such ultrasonic images of the body, it is necessary to scan the ultrasonic beams toward the inside portions of the body.
Various scanning systems have been proposed; typically, a mechanical scanning system, a linear scanning system, and a sector scanning system.
In the linear scanning system, the transducer is constructed with a plurality of transducer elements arranged in an array. These elements are electrically divided into plural sub-groups. During the beam transmission, the transducer element sub-groups are sequentially excited and the ultrasonic beams are scanned while steering and focusing the ultrasonic beams are controlled by giving predetermined delay times to the exciting signals.
The conventional delay mechanism employs the analogue delay lines having a number of coils and capacitors, with various types of switching mechanism for selectively switching these delay lines. The delay lines are so-called "analogue delay lines."
Another conventional delay mechanism is known from, e.g., U.S. Pat. No. 4,290,310 to Anderson issued on Sept. 22, 1981, which discloses the digital control and memory means for both steering and focusing of the transmitter and receiver portions.
It is an object of the present invention to realize highly precise delay times for steering and focusing the ultrasonic beams by introducing a digital control technique.
It is a further object of the present invention to provide an ultrasonic imaging apparatus incorporating a digitally-operated delay circuit without employing higher frequency circuit elements.